Method of coating fibrous surfaces



Patented Jan. 14, 1947 METHOD OF COATING FIBROUS SURFACES Clarence Walter Wilson, Norco, Calif., assignor to California Fruit Growers Angeles, Calif., a corporation of California Exchange, Los

No Drawing. Application February 17, 1942,

Serial No. 431,300

2 Claims. (chum-60) This invention relates. in general, to methods of coating surfaces. More particularly the invention relates to the coatin of fibrous surfaces with a coating which I may call a stop coat, that is, a protective film which tends to fill up or seal the minute pores of the fibrous material. and which also tends to lay and cover the fibers thereof. As examples of fibrous materials I mean paper and paper-like materials, fiberboard, wood surfaces, finely woven cloth, etc.

This application is a continuation-in-part of my co-pending application Serial No. 353,125, filed August 17, 1940, which application relates particularly to reducing and preventing the tendenoy of surfaces such as those of asphalt. bitumen, highly concentrated molasses, tacky rubber, and the like. to stick to other surfaces, particularly the fibrous surfaces of materials such as wood. paper, etc. The present application relates broadly to the treatment of fibrous surfaces, including those just mentioned, for the purpose of preventing them from sticking to sticky surfaces such as asphalt, bitumen, highly concentrated molasses, and the like, and it includes improved methods for treating such fibrous surfaces for this purpose. It also relates more specifically to the provision of methods of treating these fibrous surfaces with a film or stop coat to render the surfaces so treated more impervious to oleaginous substances.

A stop coat is used in connection with fibrous surfaces in order to reduce the tendency of such surfaces to adhere or to stick to other surfaces, part cularly tacky or sticky surfaces, and, more specifically, it is used to make the fibrous surfaces substantially impervious to the passage of materials thereinto and therethrough. The stopcoating of fibrous surfaces is desirable when those materials having fibrous surfaces are used in connection with the handling of such sticky articles as asphalt, bitumen, and pitch-like substances, as well as highly concentrated molasses and the like. Also, in many instances it is desirable to apply a stop coat to fibrous materials such as paper and paper-like materials, as, for example, when these are to be used to package such articles as cheeses, bakery goods, etc., from which oleaginous substances tend to exude and permeate the paper. Again, a stop coat finds application in connection with the preparation of paper and paper-like material prior to printing, in order to reduce ink permeation and diffusion.

The problem of coating fibrous surfaces, such as those mentioned above, with a protective film, is one which has been attacked over a long period 2 of time and from many different angles, but up to the present still remained, for the most part, unsolved. Although many substances or combinations of substances have been suggested as possible coatings for fibrous material in order to make them satisfactory for packaging such materials as asphalt, bitumen, or such oleaginous materials as bakery goods, cheeses, and confections, as well as greases and oils themselves, none has been completely successful.

Probably the greatest difficulty has arisen in the preparation and application of an impervious and continuous film which will remain intact under conditions of fabrication and use. I have found, for example, that those films which have been satisfactoryto lay and cover the fibers of a fibrous surface have often times not exhibited satisfactory impermeability under more trying conditions. On the other hand stop coats or films which have been ordinarily satisfactory for some uses failed to be sufficiently elastic to permitdistortion or creasing. In addition to the requirements that a stop coat or protective film must satisfactorily cover and lay the fibers, the stop coat should be flexible or elastic enough to permit fabrication of containers therefrom while remaining intact, or nearly so, itself. Also the stop coat should notpermeate to any appreciable extent the fibrous material being coated, since it would require more material to give a satisfactory film and in addition there is then a tendency toward the formation of pits and holes in the film.

I have now discovered methods whereby it is possible to apply a stop coat to fibrous surfaces which will permit the use of these materials in conjunction with adhesive substances, such as asphalt, bitumen, highly concentrated molasses, etc., and which will allow the so-treated fibrous materials to be readily removed from the asphalt, bitumen, etc. Furthermore I have discovered methods by which I can coat fibrous surfaces with a protective film so as to make them substantially impermeable to greases and inks. Furthermore, and perhaps of greatest importance, I have discovered methods of coating fibrous materials, such as paper and paper-like materials with a satisfac tory stop coat so that the so-treated fibrous materials may be fabricated satisfactorily into packages or containers without impairing the protective film. i Generally stated, my invention involves the preparation of a material to be used as a stop coat or protective film, as well as the method of satisfactorily applying said protective film to the fibrous surfaces to be coated. The basic ingredient of my stop coat or protective film is a material commonly referred to as a pectate. The pectate is usually made into and applied in the form of an aqueous dispersion. Accordingly, an object of my invention is to provide and disclose methods of coating fibrous surfaces with a protective film containing a pectate so as to render the coated material useful in the packaging of such adhesive materials as asphalt, bitumen, and the like.

Another object of this invention is to provide and disclose methods of stop coating 5. fibrous surface with a protective film containing a pectate, as an effective ingredient, which film is resistant to permeation by oleaginous materials.

A further object of this invention is to provide and disclose methods of coating paper and paper-like materials with a protective film containing a pectate which film is non-penetrating, nontoxic, and comparatively tough and elastic, and which will effectively fill or seal minute pores of the paper-like material, and will be resistant to permeation by oleaginous materials.

Other objects, uses, and advantages will appear more fully and at large hereinafter, and

with the fibrous pectates, such as those described I in U. S. Patent Re. 21,077. Ordinarily I choose to use fibrous sodium pectate, although other fibrous pectates may be satisfactorily used.

Also I may use those pectates which may be prepared in accordance with U. S. Patent No. 1,410,920.

In my co-pending application previously referred to, I have disclosed methods and means whereby the tendency of surfaces such as asphalt, bitumen and the like to stick to other surfaces, and particularly fibrous surfaces, is materially reduced by coating the surface with a film containing pectate. The treatment of fibrous surfaces in the manner therein disclosed is satisfactory to reduce the sticking tendency of asphalt and the like to fibrous surfaces, to a point representing commercial utility. For example, a wooden barrel may be treated in accordance with the methods therein disclosed, and the asphalt subsequently poured thereinto will be effectively prevented from sticking to the inside of the barrel. However, I have found that such treatment as is disclosed there does not produce a coated fibrous surface which is completely satisfactory for use with oleaginous materials in general, including those which tend to continue exuding grease and grease-like materials after packaging. I find that in some instances, and for certain surfaces, the films formed in accordance with the methods described in my co-pending application tend to have weak spots or pinholes which allow the oleaginous exudate to permeate the treated materials. The pinholes and weak spots cause very little trouble when packaging materials such as asphalt, bitumen and the like, which materials tend to harden on cooling, with diminishing oleaginous exudation. With greases, oils, etc., however, the tendency toward permeation of the package material is ever present.

In theorizing, Lbelieve that these weak spots and pinholes are a result of air being entrapped in the voids of the fibrous surface being treated with the pectate film, and that when the film dries, these minute air bubbles or pockets expand, or the drying coating draws down away from the tops of the bubbles, making thin spots in the film which under stress tend to break, or perhaps even break during drying, in either case causing pinholes. Consequently the film is not substantially continuous and, therefore, permits some permeation of oils, grease, and grease-like materials. This difiiculty is more pronounced when coarse fibrous surfaces are treated.

I have discovered, however, that if I first condition the fibrous surfaces before I apply the protective pectate film I am able to overcome the difficulties above described, wherever they occur.

In applying the invention to the use on fibrous surfaces such as paper, I find it advantageous to apply the stop coat to the finished paper. However, as just stated, before the protective'film is applied to the fibrous surface, particularly to a porous-surfaced paper, I find it advantageous to first condition the surface thereof. To condition the fibrous material, the surface thereof may, for example, be completely wet with water. This may be satisfactorily accomplished by spraying water onto the surface of the material being conditioned. The amount'of water necessary to condition the surface will, of course, depend on the fibrousness of the surface being treated. The more fibrous the surface, the more conditioning will be required. When relatively more highly finished surfaces are being coated I have found that relatively less water will 'be required in order to completely wet and thereby condition the surface. Presumably, continuing with the explanation set out above, the water eliminates, or substantially eliminates, from the surface voids the air that would be entrapped there by the much more viscous pectate solution, and thus presents to the pectate solution as it is being applied a temporarily'smooth, relatively air-free surface. With papers already presenting a smooth surface substantially free from air pockets by reason of having already been sufficiently sized and/or calendered, no additional conditioning will be required prior to coating.

In making use of the invention in connection with paper material, I find it advantageous to apply the protective film or stop coat to the paper. As previously mentioned, I may use the crude pectate pulp described in U. S. Patent Re. 21,077, or the purified pectate also therein described.

Employing the crude pectated pulp described in the above-mentioned patent, I make the dry mixture containing dry pectated pulp, sodium pyrophosphate, and sodium carbonate. Since there may exist some variation'in the crude pectated pulp, due to different lots of fruit, etc., I find it desirable to mix the dry pectated pulp with an amount of NarPzO-z falling within the range of from about 5.0% to 10.0% based on the weight of the pectated pulp. The sodium carbonate is added in an amount sufiicient to give a pH in the final pectate dispersion of above 7.5. Ordinarily this amount will be approximately 5% of the weight of the pectated pulp in the dry mixture. v

To an appropriate quantity of hot, and preferably boiling, water I add sufficient of the pectated pulp mixture to give the desired concentration of pectate in the dispersion. I prefer to boil the dispersion mixture with rapid agitation for about 5 minutes in order to insure substantially complete dispersion of the pulp. The dispersion is then ready for use but it may preferably be somewhat cooled before application. It may be applied to the conditioned surface in any desired manner, as by spraying, dipping, brushing, or rolling. In applying the peetate dispersion to the surface of the paper, I have found that a dispersion containing about 2.0%of the pectated pulp by weight goes on very readily and gives a uniform, coated surface designed to give a protective film. On the other hand, a dispersion of 6.0% by weight of pectate produces a coating of a thickness very satisfactory under some circumstances.

After the film is applied, the paper is then dried. It may be formed into containers, as desired. Such paper coated in accordance with the above disclosure may be constituted into containers to receive such adhesive materials as asphalt, bitumen, and the like.

As a further example of the methods and means of stop coating fibrous surfaces, I may proceed in accordance with the following example:

Using a kraft paper as an example of the fibrous material to be coated, I find it advantageous to apply the stop coat to the finished paper after the paper has been conditioned. I have found that about 100 ounces of water will satisfactorily condition 1000 square feet of paper. After the paper has been conditioned, and before any appreciable drying has taken place, the peetate dispersion is applied to the surface in any convenient manner. as by spraying. Suitable application may also be made by brushing or by a doctor blade.

In preparing the pectate dispersion a quantity of pectated pulp is mixed with the sodium carbonate and sodium pyrophosphate in accordance with the previous disclosure. I have found, however, that ordinarily the following proportions by weight may be conveniently used.

Parts Crude pectated pulp 20.0 Sodium carbonat 1.5 Sodium pyrophosphate 1.0

Using the above dry mixture as the base for the preparation of the aqueous dispersion, one part of the dry pectated pulp mixture is added to 20 parts of boiling water with stirring. The stirring should be of the type which preferably keeps the resulting dispersion as free from air as possible, and should be continued until the pectated pulp is completely disintegrated. If considerable quantities of air are beaten into the dispersion by the agitation, it may be desirable to deaerate the dispersion, depending upon the method of applieation of the dispersion. After substantially complete dispersion of the pulp has been obtained, the dispersion may be screened to remove any large, undispersed particles. I have found it desirable to pass the dispersion through a screen of about 100 mesh in order to remove any remaining coarse particles of pectated pulp and any undispersed pectated pulp. If, however, the pectated pulp is finely ground, and the dispersion complete, this step of screening may not be necessary. Other satisfactory means of removing the coarse particles of pectated pulp, or any in dispersed pectated pulp, may be used, as for example centrifuging.

The above dispersion, on cooling or while warm, as previously described, may be used to coat the paper where it is desired to use the paper in connection with the packaging of substances or materials tending to adhere thereto, or those materials which tend to exude oleaginous materials. If the paper is to be subsequently creased or severly distorted, I find it desirable to add a plasticizer to the dispersion prior to the application of the dispersion to the paper.

As examplesof suitable plasticizers, I may use glycerol orsorbitol. A mixture of glycerol and urea is also satisfactory as a plasticizer. The plasticizer is preferably added to the dispersion, although it may be sprayed over the pectate film after application. The glycerol maybe used in an amount of about based on the weight of pectated pulp in the dispersion. When a mixture of glycerol and urea is used, I have found it satisfactory to add the glycerol to the dispersion in an amount equal to about 30% of the weight of the pectated pulp in the dispersion. The urea is added in an amount equal to about based on the weight of the pectated pulp in the dispersion.

When applying the dispersion to the surface of paper or like material, I have found that a satisfactory coating will be obtained if the dispersion is applied in amounts not less than A pound of pectate per 1000 square feet of paper. Larger amounts of pectate may be used if necessary. Also, if desired, more than one coat may be applied to the paper, although adequate time should be allowed between applications for the drying of the previous coat.

If desired, both sides of the fibrous material being treated may be coated with one or more coats.

After drying the coated material may be formed into containers if desired. It is also to be noted that the stop coat or protective film may be applied to preformed containers. These applications may easily be madeby spraying pectated pulp dispersion over the surface of the container.

For some purposes I find it desirable to add to the pectate dispersion an adhesive such as ordinary glue, or other suitable adhesive, which manifestly should be water-soluble. The adhesive seems particularly desirable if the coated fibrous material is to be subsequently printed, for, in certain types of printing and similar operations the surface of the paper, perhaps in its entirety,

, or perhaps in more or less isolated spots, may be subjected to considerable pull, and any tendency which any such operation might have to loosen the surface coating should be carefully guarded against About 30% glue based on the weight of the crude pectated pulp in the dispersion seems to improve thestop coat. Larger amounts of glue may be desirable under some circumstances.

If purified fibrous pectates referred to in Reissue Patent No. 21,077 are used, it should be pointed out that it will not be necessary to use the alkaline ingredients such as sodium carbonate and sodium pyrophosphate as dispersion aids. It should be kept in mind that a lesser quantity of purified pectate will be required. Since the crude pectated pulp usually contains about 30% pectate ordinarily, only about one third a much of the purified pectate will be required for an equivalent dispersion, as when. using the crude pulp. In other respects the formula given for the crude pectated pulpis satisfactory when using the purified fibrous pectate.

Having thus described my invention in such clear, concise, and exact terms as to enable others 7 skilled in the art to make and use the same, I claim as my invention and desire to secure by Letters Patent the following:

1. A method of treating paper which is normally pervious to oleaginous materials to render the same substantially impervious to such materials comprising, conditioning the surface of said paper by wetting the same with water and before any appreciable drying has taken place forming on the conditioned paper a substantially continuous film containing a fibrous pectate in an amount not less than /2 poundoi .pectate per thousand square feet of surface. I

2. A method of treating material having a librous surface comprising, conditioning said ma-.

terial by Wetting the surface thereof with water and before any appreciable drying has taken place forming on the conditioned surface a substantially continuous film containing a fibrous pectate in an amount not less than pound of V 10 pectate per thousand square feet of surface.

CLARENCE WALTER WILSONK 

